A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head, which is housed in a slider, and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies in part on a suspension's force on the slider and on the aerodynamic characteristics of the slider air bearing surface (ABS) to provide the proper distance between the read/write head and the surface of the magnetic-recording disk (the “flying height”) while the magnetic-recording disk rotates. A slider therefore is said to “fly” over the surface of the magnetic-recording disk.
Increasing areal density (a measure of the quantity of information bits that can be stored on a given area of disk surface) is one of the ever-present holy grails of hard disk drive design evolution, and has led to the necessary development and implementation of various means for reducing the spacing between the magnetic head and the magnetic-recording disk. Thus, modern head sliders are flying closer and closer to the disk and it is increasingly important to precisely detect the flying height.
In some instances, the mechanical vibration of the head slider is used to detect contact between the slider and the disk, because contact awareness is important to accurate flying height spacing. For more accurate contact detection, a dedicated contact sensor (also at times referred to as an “embedded contact sensor” or “ECS”, and a “resistive temperature detector” or “RTD”) has been proposed, which is configured into the head slider and whose temperature change is used as an indicator of contact and/or near contact. ECS elements sense physical contact of the slider with the disk based on the ECS element's resistance, e.g., the amount of voltage across the element, which is affected by the temperature change caused by such physical contact.
However, to monitor the resistance change in this manner it is necessary to apply current to the contact sensor. Consequently, an additional electrical line is needed on the suspension and an additional electrical connection pad is needed on the slider in order to utilize such a contact detection system. This results in a more complex and costly design in comparison with a magnetic head slider that does not comprise a contact detection system.